Light emitting devices using III-V compound semiconductors are known. Examples are a red light emitting device made of an AlGaAs-based material or AlGaInP-based material formed on a GaAs substrate, an orange or yellow light emitting device made of a GaAsP-based material formed on a GaP substrate, and an infrared light emitting device made of an InGaAsP-based material formed on an InP substrate.
Light emitting devices are classified into, for example, a light emitting diode (LED) using spontaneous emission light, and a laser diode (LD) or semiconductor laser having an optical feedback function for extracting stimulated emission light. Light emitting devices can be used as, for example, a display device, communication device, high-density optical recording light source device, high-accuracy optical processing device, and medical device.
Particularly from the 1990s, high-efficiency blue and green LEDs using InxAlyGa(1-x-y)N-based, III-V compound semiconductors (0≦x≦1, 0≦y≦1, and 0≦x+y≦1) containing nitrogen as a group-V element have been realized.
In addition, an LED having a high efficiency even in an ultraviolet region has been realized by the later research and development, and a blue LD has also been put on the market.
Increasing the output and efficiency of particularly the ultraviolet or blue LED has a large industrial significance. A white LED can be realized by integrating the high-output, high-efficiency blue or ultraviolet LED with a phosphor. The white LED is regarded as promising in illuminating applications.
To increase the output, that is, to improve the total radiant flux of a light emitting device, it is essential to increase the size of the light emitting device and secure a high robustness against a high input power. Also, a large-area light emitting device has the emission characteristics of an area source, and is particularly suitable for illuminating applications.
In a light emitting device obtained by simply increasing the area of an ordinary small-sized light emitting device while maintaining its structure, it is difficult to make uniform the emission intensity in the entire light emitting region.
Various attempts have been made to increase the in-plane uniformity of the emission intensity of a light emitting device. For example, attempts to increase the in-plane uniformity of the emission intensity of a single light emitting device are disclosed in patent references 1 to 4. Each of patent references 1 to 4 has disclosed a light emitting device having a structure in which one electrode (an outer electrode) completely surrounds the whole circumferential surface of the other electrode (an inner electrode).
On the other hand, to provide area light sources, patent references 5 to 7 have disclosed light emitting devices in each of which a plurality of light emitting portions are arranged on one substrate.    Patent reference 1: Japanese Patent No. 3,136,672    Patent reference 2: Japanese Patent No. 3,244,010    Patent reference 3: Japanese Patent Laid-Open No. 2002-319705    Patent reference 4: Japanese Patent Laid-Open No. 10-209496    Patent reference 5: Japanese Patent Laid-Open No. 11-150303    Patent reference 6: Japanese Patent Laid-Open No. 2002-26384    Patent reference 7: Japanese Patent Laid-Open No. 2003-115611